Oskar Pfungst

Oskar Pfungst (1874 to 1932) was a German comparative biologist and psychologist best remembered for his investigation of Clever Hans, a horse that appeared able to solve a wide range of arithmetic problems set by its owner. While working as a volunteer assistant in the Berlin laboratory of Carl Stumpf, Pfungst was asked to look into the horse, and after a formal investigation in 1907 he showed that the animal was not performing intellectual tasks but was watching the involuntary body language of the people around it, including a trainer who was entirely unaware that he was giving cues. The artefact he identified is now called the Clever Hans effect, and it remains important to discussions of the observer effect in research methodology and of animal cognition. Pfungst never earned an advanced academic degree, although he later received an honorary medical doctorate from the University of Frankfurt, where he lectured, and according to Zusne he published only about fifteen titles in his career.